Propulsion system

ABSTRACT

A propulsion system comprises of a flow passage ( 173 ) having an intake ( 175 ) for communicating with a source of working fluid such as seawater and an outlet ( 177 ). A mixing zone ( 209 ) is disposed within the flow passage ( 173 ) between the intake ( 175 ) and the outlet ( 177 ). An injection means including annular nozzle ( 217 is provided for injecting a hot compressible driving fluid ( 175 ) such as steam into the mixing zone ( 209 ) in a flow direction towards the outlet ( 177 ). The arrangement is such that the interaction between the steam and the seawater in the mixing zone ( 207 ) develops a pressure reduction in the mixing zone ( 207 ) to cause seawater to be drawn from the source into the mixing zone ( 207 ) and propelled towards the outlet ( 177 ). A marine drive unit incorporating the propulsion system is also claimed. A heat recovery system comprising a refrigerant circuit with a heat exchanger for extracting heat from a heat source to vapourise a refrigerant in the circuit and means to convert heat energy in the vapourised refrigerant to torque and, a nozzle means ( 217 ) having an inlet, an outlet ( 177 ) and a flow passage ( 173 ) the size of which is selectively variable are also disclosed.

FIELD OF THE INVENTION

[0001] This invention relates to a propulsion system.

[0002] The invention has been devised particularly, although not solely,as a propulsion system for propelling watercraft. In such anapplication, a propulsive force for the watercraft typically arises fromgeneration of a jet of water which imparts thrust to the watercraft.However, the propulsion system may have other applications; for example,the propulsion system may be used to propel a stream of liquid in themanner of a pump. Such a use may have particular application in, forexample, fire-fighting where a stream of water is propelled onto a fire.

BACKGROUND ART

[0003] Various systems are known for propelling watercraft, includingmotor-driven propellers, and jet propulsion units which produce thrustby discharge of a stream of fluid.

[0004] Jet propulsion units are becoming increasingly popular inpleasure and commercial craft because of their shallow draft capabilityand reduced maintenance requirements in comparison to conventionalpropeller propulsion system.

[0005] U.S. Pat. No. 3,402,555 (Piper) discloses a steam jet nozzlesystem for propelling watercraft. In the nozzle system, steam isgenerated and discharged under high pressure to provide propulsion. Thenozzle system includes a nozzle having an entrance end and an exit end.Steam enters the nozzle through the entrance end. Raw water from thebody of water through which the watercraft is to be propelled isintroduced into the nozzle so as to be converted into steam tosupplement the steam already in the nozzle. The propulsion is notprovided by a jet stream of water but rather by generation and dischargeof steam under high pressure.

[0006] A known water-jet propulsion unit for watercraft is produced byHamilton Jet in New Zealand. A water-jet propulsion unit of this typeutilises an engine-driven impeller to draw water through a suction footopening onto the underside of the watercraft and to discharge the waterunder pressure through a discharge port and thereby propel thewatercraft. The impeller is typically driven through a drive shaft froman internal combustion engine. The use of an impeller in a conventionalwater-jet propulsion system has several disadvantages, includingcavitation and other efficiency limitations. Furthermore, there is asignificant loss of heat energy from the internal combustion engine usedto drive the impeller.

[0007] There have been various proposals directed to propulsion ofwatercraft using a stream of water driven by a high pressure fluid toprovide thrust. The high pressure fluid imparts momentum to the waterstream which discharges as a water jet. Typically, such proposalsinvolve a duct providing a flow passage having an intake and an outlet,with both the intake and the outlet being open to the water throughwhich the watercraft is to be propelled. The high pressure driving fluidis injected into the duct to contact water in the duct and therebytransfer momentum thereto, causing a stream of water to flow through theduct and discharge as a jet from the outlet to provide propulsivethrust. One such arrangement is disclosed in U.S. Pat. No. 5,344,345(Nagata) wherein the driving fluid comprises pressurised water andcompressed air. Another such arrangement is disclosed in U.S. Pat. No.5,598,700 (Varshay) where the driving fluid comprises a compressed gas.

[0008] The present invention seeks to provide a propulsion system forgenerating a fluid stream utilising a driving fluid without relyingsolely on momentum transfer.

DISCLOSURE OF THE INVENTION

[0009] According to one aspect of the present invention there isprovided a propulsion system comprising a flow passage having an intakefor communicating with a source of working fluid and outlet, a mixingzone disposed within the flow passage between the intake and the outlet,means for introducing a hot compressible driving fluid into the mixingzone, whereby interaction between the driving fluid and the workingfluid in the mixing zone develops a pressure reduction in the mixingzone to cause working fluid to be drawn from said source into the mixingzone and propelled towards the outlet, and means for aerating theworking fluid with an aerating gas prior to interaction of the drivingfluid in the mixing zone whereby a three-phase fluid regime is createdin the mixing zone by virtue of the interaction of the aerating gas, theworking fluid and the driving fluid.

[0010] The compressible driving fluid is hot in the sense that it is ata temperature greater than the temperature of the working fluid enteringthe mixing zone. Typically, the driving fluid is at a temperature of atleast 50° C. above the temperature of working fluid and preferably morethan about 70° C. above the temperature of the working fluid.

[0011] The interaction between the hot compressible driving fluid andthe working fluid involves contact of driving fluid with the workingfluid causing rapid cooling of the driving fluid to produce the pressurereduction in the mixing chamber. The rapid pressure reduction is ineffect an implosion within the mixing zone. The feature of the drivingfluid being compressible allows for a volumetric change upon rapidcooling of the driving fluid.

[0012] The interaction between the hot compressible driving fluid andthe working fluid preferably also involves momentum transfer from thedriving fluid to the working fluid.

[0013] It is believed that contact between the driving fluid and theworking fluid at the mixing zone within the flow passage may also causeliberation of gases (and oxygen in particular) from the working fluidwhen the latter is a liquid, and in particular water. The liberatedgases may assist in momentum transfer from the driving fluid to theworking fluid. Furthermore bubbles of the liberated gases may expandupon being heated in the mixing zone and in doing so apply pressure, andthus work, to the working fluid so further assisting propulsion of theworking fluid towards the outlet. Additionally the liberated gases mayserve to reduce skin friction between the working fluid and thesurrounding boundary of the flow passage.

[0014] As alluded to above, the working fluid may comprise water, andsaid source may comprise a body of water. In the case of a propulsionsystem for watercraft, the working fluid would comprise water drawn froma body of water in or on which the watercraft is accommodated. In such acase the body of water is typically a lake, a river, an estuary or thesea.

[0015] The compressible driving fluid may comprise a substantiallygaseous fluid capable of rapid pressure reduction upon exposure to thecooling influence of the working liquid. The gaseous fluid may comprisea gas or a gaseous mixture. Further, the gaseous fluid may haveparticles such as liquid droplets entrained therein.

[0016] The driving fluid may, for example, comprise a condensable vapoursuch as steam, or exhaust gases from a combustion process such as in aninternal combustion engine or a gas turbine.

[0017] Steam is a particularly suitable driving fluid, as it can begenerated readily and efficiently. Furthermore, steam can be expandedeasily and is capable of rapid volume reduction upon condensation togenerate the necessary implosion effect.

[0018] Steam is a particularly appropriate form of driving fluid wherethe working fluid is water. In such a case, the source from which thewater is drawn as the working fluid may also supply water from which thesteam is generated. Additionally, because of the relationship betweensteam and liquid water, where steam is the evaporated phase of water,there is no undesirable contamination of the water used as the workingfluid upon contact with steam used as the driving fluid. This can beimportant where the propulsion system is used for propelling watercraftthrough a body of water, as it avoids pollution of the body of water bythe driving fluid.

[0019] The driving fluid can also be a multi-phase fluid, such as amixture of steam, air and water droplets. The air and water droplets canbe in the form of a mist. Such a multi-phase fluid provides the benefitof increasing the mass flow rate of the driving fluid. Additionally, itserves to increase the density of the driving fluid, bringing it closerto the density of the working fluid to thereby enhance momentumtransfer. Momentum transfer is more effective the closer the density thedriving fluid is to the density of the working fluid.

[0020] During operation of the propulsion system, the driving fluid maybe injected into the working fluid on a continual basis or on anintermittent basis such as in a pulsed fashion.

[0021] The flow rates of the driving fluid and the working fluid may beselected according to the desired flow rate of working fluid dischargingat the outlet. Where the driving fluid is steam and the working fluid iswater, mass flow rates of steam to water in a ratio ranging from about1:10 to 1:150 have been found to be effective within the operating rangeof the propulsion system. Other ratios may, however, also be effective.

[0022] The aerating gas may comprise air or any other appropriate gas orgaseous mixture. Aeration of the working fluid produces a two-phasemixture which has some compressibility. It is believed that the aerationhas the effect of lowering the density of the two-phase mixture incomparison to the working fluid, so assisting in the transfer of theworking fluid along the flow passage towards the mixing chamber. Thelower density of the two-phase mixture is also advantageous as thedensity is closer to the density of the driving fluid, so assistingmomentum transfer. Momentum transfer is increased as the density of thetwo phase mixture approaches the density of the driving fluid. Theaeration process may also reduce skin friction between the working fluidand the surrounding boundary of the flow passage. Additionally, theaeration process may assist in momentum transfer from the driving fluidto the working fluid. Furthermore, bubbles of the aerating gas in theworking fluid receive heat from the working fluid, the working fluiditself having been heated through heat exchange as a result of contactwith the hot driving fluid. Additionally, there may be direct contactbetween the hot driving fluid and the bubbles of aerating gas for heatexchange. The heated gas bubbles expand upon exiting the mixing zone andin so doing apply pressure, and thus work, to the working fluid sofurther assisting propulsion of the working fluid towards the outlet.

[0023] The section of the flow passage between the intake and the mixingzone may be of any suitable profile including the profile of a divergentnozzle. Such a profile may assist the aeration process, particularly bydrawing the aerating gas into the flow passage.

[0024] The aerating gas introduced into the working fluid during theaeration process may be by way of an open draw or it may be regulated inorder to achieve the desired level of aeration. An open draw isparticularly suitable where the aerating gas is air, as it can simply bedrawn from the surrounding environment. The regulation may be achievedin any suitable way such as by restricting the flow of aerating gas (forexample by way of a valve) or enhancing flow of the aerating gas bydelivering it under pressure.

[0025] The extent of aeration required may be selectively varied toinfluence the extent of thrust produced at the outlet.

[0026] Where the working fluid is water and the aerating gas is air, ithas been found that the required volume of air to water is not more thanabout 1:10 by volume. In certain operating conditions, the requiredvolume of air to water can be relatively low, typically in the ratio ofabout 1.300 by volume.

[0027] The section of the flow passage between the intake and the mixingzone may comprise an intake chamber terminating at a discharge openinghaving a cross-sectional area smaller than the cross-sectional area ofthe mixing zone at the location where the discharge opening opens ontothe mixing zone Such an arrangement accommodates expansion of theworking fluid into the mixing zone, as is particularly beneficial in thecase where the working fluid is a liquid which has been aerated.

[0028] The section of the flow passage defining the mixing zonepreferably progressively contracts in the direction of fluid flow so asto accelerate the flow of working fluid towards the outlet and alsoassist in the momentum transfer from the driving fluid to the workingfluid. Preferably, the mixing zone contracts to a size which creates achoked condition in the fluid flow passage.

[0029] The injection means for injecting the driving fluid into themixing zone may comprise a nozzle means.

[0030] The type of nozzle means utilised depends on the propulsionrequirements.

[0031] In one arrangement, the nozzle means may comprise a single nozzleor a plurality of nozzles located at spaced intervals along the mixingchamber in the direction of flow of the working fluid.

[0032] The nozzle means may be configured as a subsonic, sonic orsupersonic nozzle. It is however advantageous for the nozzle means to beconfigured as a supersonic nozzle to provide greater thrust.

[0033] The nozzle means is preferably disposed adjacent to a boundarysurface of the flow passage.

[0034] In one arrangement, the nozzle means may extend around aperimeter of the flow passage. In such an arrangement, the nozzle meansmay comprise a nozzle passage of annular configuration. The annularpassage may, for example, be defined between first and second membersselectively movable relative to each other for varying the size of thenozzle flow passage. The first member may define the mixing zone and thesecond member may define the intake passage opening onto the mixingzone, with the annular nozzle passage being disposed around thedischarge opening of the intake passage

[0035] In another arrangement, the nozzle means may comprise a nozzlepassage configured as a slit. In such an arrangement, the slit may bedefined between two spaced apart nozzle elements

[0036] The two nozzle elements may be movable relative to each other forselectively varying the size of the nozzle passage therebetween.

[0037] Preferably, a nozzle control means is provided for effectingmovement of the nozzle sections relative to each other. Typically, onenozzle element is fixed and the other is selectively movable under theaction of the nozzle control means.

[0038] The flow passage may have an outlet section extending from themixing zone and terminating at the outlet, with the outlet section beingconfigured as a diffuser. This arrangement is particularly suitablewhere the mixing zone contracts to an extent that creates a choked flowcondition in the fluid flow, as mentioned previously. Preferably athroat is defined between the mixing zone and the outlet section. Wherethere is a choked flow condition, it is typically established at thethroat. The flow passage may comprise a portion defined between twoopposed surfaces, at least one of which is selectively movable relativeto the other for varying the cross-sectional area of the portion of theflow passage defined therebetween. Preferably said portion terminates atthe outlet and includes the outlet section.

[0039] In one arrangement, the two opposed surfaces are planar surfaces.Preferably, the two opposed surfaces are angularly movable relative toeach other. This may be achieved by one of the opposed surfaces beingpivotally mounted with respect to the other surface.

[0040] Preferably, a control means is provided for selectivelycontrolling relative movement between the two opposed surfaces.

[0041] Means may be provided for selectively diverting the driving fluidthereby causing it to flow in a reverse direction along the flow passageto discharge outwardly through the intake In this way, the propulsionsystem may be utilised to provide reverse thrust.

[0042] Means may be provided for selectively varying the size of theintake.

[0043] According to a further aspect of the invention there is provideda propulsion system comprising a flow passage having an intake forcommunicating with a source of working liquid and an outlet, a mixingzone disposed within the flow passage between the intake and outlet,aeration means for aerating the working liquid with an aerating gasbefore delivery thereof to the mixing chamber, and a nozzle means forintroducing a jet of hot compressible driving fluid into the mixing zonein a flow direction towards the outlet whereby a three-phase fluidregime is created in the mixing zone by virtue of the interaction of theaerating gas, the working liquid and the driving fluid, and wherebyinteraction between the driving fluid and the working liquid in themixing zone develops a pressure reduction relative to the intakepressure to cause working liquid to be drawn from said source into themixing zone and propelled towards the outlet.

[0044] Aeration of the working liquid produces a two-phase mixture whichhas some compressibility.

[0045] According to a further aspect of the invention there is provideda propulsion system comprising a flow passage having an intake forcommunicating with a source of working fluid and an outlet, a mixingzone disposed within the flow passage between the intake and outlet, anda nozzle means for injecting a condensable vapour into the mixing zonein a flow direction towards the outlet, whereby interaction between thecondensable vapour and the working liquid in the mixing zone causes thevapour to condense providing a volume reduction to create a suctioneffect to cause working liquid to be drawn from said source into themixing zone and propelled towards the outlet, and means for aerating theworking fluid with an aerating gas prior to interaction of the drivingfluid in the mixing zone whereby a three-phase fluid regime is createdin the mixing zone by virtue of the interaction of the aerating gas, theworking fluid and the condensable vapour.

[0046] According to a still further aspect of the invention there isprovided a propulsion system for a watercraft accommodated on or in abody of water, the propulsion system comprising a flow passage having anintake for communicating with the body of water and an outlet, a mixingzone disposed within the flow passage between the intake and outletwhereby a stream of water drawn from the body of water through theintake as a working fluid can enter the mixing zone, and an injectionmeans for injecting a hot compressible driving fluid into the mixingzone in a flow direction towards the outlet, whereby interaction betweenthe driving fluid and the water in the mixing zone.

[0047] The propulsion system can be provided at any suitable location onthe watercraft. It is particularly convenient to locate the propulsionsystem in such a way that the outlet is located adjacent the stern ofthe watercraft so as to provide stern thrust to the watercraft. However,the propulsion system can be so located as to provide bow thrust to thewatercraft, or indeed it can be located such that the outlet dischargesat any location between the bow and the stern of the watercraft.

[0048] There may be a particular advantage in locating the outlet todischarge into a region below the hull of the watercraft in thatresultant aeration of water adjacent the hull of the watercraft reducesthe frictional drag effect on the watercraft.

[0049] According to a still further aspect of the invention there isprovided a watercraft having a propulsion system according to any one ofthe aspects of the invention as detailed above.

[0050] According to a still further aspect of the invention there isprovided a propulsion system for a watercraft accommodated on or in abody of water, the propulsion system comprising a flow passage having anintake for communicating with the body of water and an outlet, a mixingzone disposed within the flow passage between the intake and outletwhereby a stream of water drawn from the body of water through theintake can enter the mixing zone, and for introducing a hot compressibledriving fluid into the mixing zone, whereby interaction between thedriving fluid and the water in the mixing zone develops a zone ofreduced pressure to cause a stream of water to be drawn from the body ofwater into the mixing zone and propelled towards the outlet, and meansfor aerating the working fluid with an aerating gas prior to interactionof the driving fluid in the mixing zone whereby a three-phase fluidregime is created in the mixing zone by virtue of the interaction of theaerating gas, the water and the driving fluid, the propulsion systembeing devoid of an impeller or other mechanical device for generatingfluid flow along the flow passage to provide thrust at the outlet.

[0051] Preferably, both the intake and outlet of the propulsion systemof the watercraft are so positioned as to in use open into the body ofwater on or in which the watercraft is accommodated.

[0052] According to a still further aspect of the invention there isprovided a drive system for a watercraft, the drive system comprising apropulsion system which is as hereinbefore defined and which mayadditionally include any of the preferred features detailed above.

[0053] According to a still further aspect of the invention there isprovided a drive system for a watercraft adapted to be accommodated onor in a body of water, the drive system comprising a steam generator forgenerating a supply of steam, and a propulsion system, the propulsionsystem comprising a flow passage having an intake for communicating withthe body of water and an outlet, a mixing zone disposed within the flowpassage between the intake and the outlet whereby a stream of waterdrawn from the body of water through the intake can enter the mixingzone, and an injection means for injecting steam generated by the steamgenerator into the mixing zone in a flow direction towards the outlet,whereby interaction between the steam and the water in the mixing zonecauses water to be drawn from the body of water into the mixing zone andpropelled towards the outlet, and means for aerating the water with anaerating gas prior to interaction of the steam in the mixing zonewhereby a three-phase fluid regime is created in the mixing zone byvirtue of the interaction of the aerating gas, the water and the steam.

[0054] The drive system may further comprise a heat recovery systemadapted to recover remnant heat in the water arising from contact withthe steam.

[0055] Preferably. the steam generator comprises a boiler adapted togenerate heat from combustion of a fuel, the heat recovery means beingadapted to also recover at least some remnant heat in combustion gasesfrom the boiler.

[0056] According to a still further aspect of the invention there isprovided a method of generating a fluid flow comprising the steps of:providing a flow passage having an intake and an outlet; locating theintake of the flow passage to communicate with a source of primary fluidfrom which the fluid flow is to be established; and introducing adriving fluid into the flow passage for interacting with primary fluidin the flow passage to develop a pressure reduction at a zone in theflow passage to cause primary fluid to be drawn from said source intosaid zone and propelled towards the outlet; and further comprising thestep of aerating the primary fluid with an aerating gas prior to theintroduction of the driving fluid into the primary fluid whereby athree-phase fluid regime is created in the flow passage by virtue of theinteraction of the aerating gas, the primary fluid and the drivingfluid.

[0057] According to a still further aspect of the invention there isprovided a method of generating a fluid flow comprising the steps of:providing a flow passage having an intake and an outlet; locating theintake of the flow passage to communicate with a source of fluid fromwhich the fluid flow is to be established; and injecting a condensablevapour into the flow passage for interacting with fluid therein toprovide a volume reduction upon condensation of the vapour to create asuction effect at a zone in the flow passage to cause fluid to be drawnfrom said source into said zone and propelled towards the outlet; andfurther comprising the step of aerating the fluid with an aerating gasprior to the introduction of the condensable vapour into the fluidwhereby a three-phase fluid regime is created in the flow passage byvirtue of the interaction of the aerating gas, the fluid and thecondensable vapour.

[0058] According to a still further aspect of the invention there isprovided a method of propelling a watercraft through a body of water,the method comprising the steps of: providing the watercraft with a flowpassage having an intake and an outlet both opening onto the body ofwater; and introducing a driving fluid into the flow passage to developa pressure reduction at a zone in the flow passage to cause water fromthe body of water to be drawn through the inlet into said zone andpropelled towards the outlet as a stream for propelling the watercraft;and further comprising the step of aerating the water with an aeratinggas prior to the introduction of the driving fluid into the waterwhereby a three-phase fluid regime is created in the flow passage byvirtue of the interaction of the aerating gas, the water and the drivingfluid.

[0059] According to a still further aspect of the invention there isprovided a method of propelling a watercraft through a body of water,the method comprising the steps of: providing the watercraft with a flowpassage having an intake and an outlet both opening onto the body ofwater; and introducing a condensable vapour such as steam into the flowpassage to provide a volume reduction upon condensation of the vapourand thereby create a suction effect at a zone in the flow passage tocause water from the body of water to be drawn through the inlet intosaid zone and propelled towards the outlet as a stream for propellingthe watercraft; and further comprising the step of aerating the waterwith an aerating gas prior to the introduction of the condensable vapourinto the water whereby a three-phase fluid regime is created in the flowpassage by virtue of the interaction of the aerating gas, the water andthe condensable vapour.

[0060] Each aspect of the invention as set forth hereinbefore mayfurther comprise a heat recovery system for recovering heat from a heatsource. the heat recovery system comprising a refrigerant circuit havinga heat exchanger exposed to the heat source for extracting heattherefrom to vapourise a refrigerant In the refrigerant circuit, andmeans associated with the refrigerant circuit for converting heat energyin the vapourised refrigerant to torque.

[0061] The means for converting heat energy in the refrigerant vapor totorque may comprise an impeller in the refrigerant circuit upon whichthe refrigerant vapor acts.

[0062] According to a still further aspect of the invention, there isprovided a drive system for a watercraft accommodated on or in a body ofwater, the drive system comprising a propulsion system as set forthhereinbefore, a boiler for generating a supply of steam, the boilerhaving a combustion chamber and an exhaust passage along which exhaustgases from the combustion chamber are discharged, and a heat recoverysystem for recovering remnant heat in the exhaust gases, the heatrecovery system comprising a refrigerant circuit having a heat exchangerexposed to the exhaust passage for extracting heat from the exhaustgases to vapourise a refrigerant in the refrigerant circuit, and meansassociated with the refrigerant circuit for converting heat energy inthe vapourised refrigerant to torque.

[0063] According to a still further aspect of the invention, there isprovided a drive system for a watercraft accommodated on or in a body ofwater, the drive system comprising a propulsion system as set forthhereinbefore, and a heat recovery system for recovering remnant heat inthe water flowing along the flow passage after the introduction of steaminto the water, the heat recovery system comprising a refrigerantcircuit having a heat exchanger exposed to the flow passage forextracting heat from water flowing along the flow passage to vapourise arefrigerant in the refrigerant circuit, and means associated with therefrigerant circuit for converting heat energy in the vapourisedrefrigerant to torque.

[0064] According to a still further aspect of the invention, there isprovided a drive system for a watercraft accommodated on or in a body ofwater, the drive system comprising a boiler for generating a supply ofsteam, the boiler having a combustion chamber and an exhaust passagealong which exhaust gases from the combustion chamber are discharged, apropulsion system as set forth hereinbefore, and a heat recovery systemfor recovering remnant heat in the exhaust gases and in the waterflowing along the flow passage after introduction of steam into thewater, the heat recovery system comprising a refrigerant circuit havinga heat exchanger exposed to the exhaust passage and the flow passage forextracting heat therefrom to vapourise a refrigerant in the refrigerantcircuit, and means associated with the refrigerant circuit forconverting heat energy in the vapourised refrigerant to torque.

[0065] The refrigerant circuit may include an evaporator having a firstportion thereof exposed to the exhaust passage for extracting heat fromthe combustion gases passing therealong and a second portion exposed tothe flow passage for extracting heat from water flowing therealong.

[0066] According to a still further aspect of the invention there isprovided a nozzle means in accordance with a propulsion system as setforth hereinbefore having an inlet, an outlet and a flow passageextending between the inlet and the outlet, characterised in that thesize of the flow passage is selectively variable.

[0067] The nozzle means may comprise a convergent section, a throatsection and a divergent section, the convergent section extending fromthe inlet to the throat section and the divergent section extending fromthe throat section to the outlet.

[0068] The nozzle means may comprise a nozzle structure comprising twoelongate elements between which the nozzle passage is defined.

[0069] Preferably, the two nozzle elements are movable relative to eachother for selectively varying the size of the flow passage therebetween.

[0070] According to a still further aspect of the invention there isprovided a propulsion system comprising a flow passage having an intakefor communication with a source of working fluid and an outlet, a mixingzone disposed within the fluid passage between the intake and theoutlet, a nozzle means for introducing a jet of driving fluid into themixing zone in a flow direction towards the outlet, whereby interactionbetween the driving fluid and the working fluid in the mixing zonecauses working fluid to be drawn from the source into the mixing zoneand propelled towards the outlet, the nozzle means having a nozzlepassage of selectively variable size, and means for aerating the workingfluid with an aerating gas prior to interaction of the driving fluid inthe mixing zone whereby a three-phase fluid regime is created in themixing zone by virtue of the interaction of the aerating gas, theworking fluid and the driving fluid.

[0071] According to a still further aspect of the invention there isprovided a drive system for a watercraft adapted to be accommodated onor in a body of water, the propulsion system comprising a flow passagehaving an intake for communicating with the body of water and an outlet,a mixing zone disposed within the flow passage between the intake andthe outlet whereby a stream of water drawn from the body of waterthrough the intake can enter the mixing zone, and a nozzle means forintroducing a jet of driving fluid into the mixing zone in the flowdirection towards the outlet, whereby interaction between the drivingfluid and water causes water to be drawn through the intake from thebody of water and propelled towards the outlet, the nozzle means havinga nozzle passage of selectively variable size, and means for aeratingthe working fluid with an aerating gas prior to interaction of thedriving fluid in the mixing zone whereby a three-phase fluid regime iscreated in the mixing zone by virtue of the interaction of the aeratinggas, the water and the driving fluid.

[0072] According to a still further aspect of the invention there isprovided a drive system for a watercraft adapted to be accommodated onor in a body of water, the drive system comprising a steam generator forgenerating a supply steam, a propulsion system comprising a flow passagehaving an intake for communication with the body of water and an outlet,a mixing zone disposed within the flow passage between the intake andoutlet whereby a stream of water drawn from the body of water throughthe intake can enter the mixing zone, and a steam nozzle means forintroducing steam into the mixing zone in a flow direction towards theoutlet, whereby interaction between the steam and the water causes waterto be drawn into the flow passage through the intake and propelledtowards the outlet. the steam nozzle means having a flow passage ofselectively variable size, and means for aerating the working fluid withan aerating gas prior to Interaction of the driving fluid in the mixingzone whereby a three-phase fluid regime is created in the mixing zone byvirtue of the interaction of the aerating gas, the water and the steam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The invention will be better understood by reference to thefollowing description of several specific embodiments thereof as shownin the accompanying drawings:

[0074]FIG. 1 is a schematic view illustrating a drive system accordingto a first embodiment installed on a watercraft;

[0075]FIG. 2 is a partly cut-away schematic perspective view of thedrive system;

[0076]FIG. 3 is a schematic side view of a propulsion system formingpart of the drive system, with a reversing flap forming part of thepropulsion system shown in a first position;

[0077]FIG. 4 is a view similar to FIG. 3 with the exception that thereversing flap is shown in a second position;

[0078]FIG. 5 is a rear elevational view of the propulsion system,showing the outlet thereof;

[0079]FIG. 6 is a cross-sectional view of a steam nozzle structureforming part of the propulsion system;

[0080]FIG. 7 is a perspective view of the steam nozzle structure;

[0081]FIG. 8 is a schematic view of a refrigerant circuit included in aheat recovery system forming part of the drive unit;

[0082]FIG. 9 is a partly cut-away schematic view of a drive systemaccording to a second embodiment;

[0083]FIG. 10 is a sectional side view of a propulsion system formingpart of the drive system of the second embodiment;

[0084]FIG. 11 is a partly sectional schematic view of a propulsionsystem forming part of a drive system according to a third embodiment;

[0085]FIG. 12 is a schematic sectional view of a propulsion systemforming part of a drive system according to a fourth embodiment;

[0086]FIG. 13 is a schematic side view of a propulsion system formingpart of a drive system according to according to a fifth embodiment;

[0087]FIG. 14 is a schematic side view of a propulsion system formingpart of a drive system according to according to a sixth embodiment;

[0088]FIG. 15 is a schematic side view of a propulsion system formingpart of a drive system according to according to a seventh embodiment;

[0089]FIG. 16 is a perspective view of a propulsion system for a drivesystem according to an eighth embodiment, with various parts of thepropulsion system being cut-away;

[0090]FIG. 17 is a view similar to FIG. 16, except that other parts ofthe propulsion system are cut-away;

[0091]FIG. 18 is a schematic plan view of a propulsion system for adrive system according to a ninth embodiment;

[0092]FIG. 19 is a schematic fragmentary view illustrating a drivesystem according to a tenth embodiment installed on a watercraft; and

[0093]FIG. 20 is a schematic view of a propulsion system according to aneleventh embodiment functioning as a pump.

BEST MODE(s) FOR CARRYING OUT THE INVENTION

[0094] Referring to FIGS. 1 to 8 of the drawings, the first embodimentis directed to a drive system 11 for a watercraft 13 in the form of aboat having a hull 15, a bow 17 and a stern 19 including a transom 20.In this embodiment, the drive system 11 is in the form of an outboardmotor which is mounted on the transom 20 of the boat 13, although itshould be appreciated that other arrangements are possible including anon-board drive system.

[0095] The drive system 11 utilises a propulsion system 21 in accordancewith the invention, as will be described.

[0096] The propulsion system 21 has an intake 25 and an outlet 27, bothof which are located below the water line of the boat 13 so as to besubmerged in a body of water 14 on which the boat 13 is afloat. For thepurposes of this description; the boat 13 is of a type operational atsea and the water will therefore be referred to as seawater. Seawater isdrawn into the intake 25 and discharged through outlet 27 so as toimpart thrust to propel the boat 13, as will be explained later.

[0097] The propulsion system 21 uses a driving fluid, which in thisembodiment is steam.

[0098] The drive system 11 includes a steam generator 31 for generatingthe steam. The steam is generated in the steam generator 31 from heatproduced upon combustion of a fuel such as a gas.

[0099] The drive system 11 further includes a heat recovery system 33 torecover remnant heat from the steam after momentum transfer to theseawater. Additionally, the heat recovery system 33 recovers some of theremnant heat in spent combustion gases exhausting from the steamgenerator 31.

[0100] The propulsion system 21 comprises a body structure 41 defining aflow passage 43 extending from the intake 25 to the outlet 27. The flowpassage 43 includes an intake section 44, a convergent section 45, athroat section 47 and a divergent section 49. The intake section 44extends from the intake 25 to the convergent section 45. The convergentsection 45 extends from the intake section 44 to the throat section 47.The divergent section 49 extends from the throat section 47 to theoutlet 27. With this arrangement, that portion of the flow passage 43beyond the intake section 44 is broadly configured as aconvergent-divergent nozzle.

[0101] In this embodiment, the flow passage 43 is of generallyrectangular cross-section having a longitudinal extent L and a lateralextent W (as best seen in FIG. 5). The longitudinal extent L issignificantly greater than the lateral extent W so as to ensure that theflow passage 43 is of a low profile in the transverse direction.

[0102] The intake section 44 is defined by a surrounding wall structure50 which includes two opposed walls 51, 53, the spacing between which isselectively variable to permit adjustment of the cross-sectional area ofthe throat section. In this embodiment, wall 51 is an upper wall, andwall 53 is a lower wall. The surrounding wall structure 50 also includestwo further opposed walls (not shown) extending between the upper andlower walls 51, 53 so as to complete a peripheral boundary around thethroat section. The further side walls (not shown) are constructed toaccommodate relative movement between the upper and lower walls 51, 53upon adjustment of the cross-sectional area of the inner section. Anadjustment mechanism (not shown) is provided for selectively adjustingthe spacing between the upper and lower walls 51, 53 by movement of thewalls towards or away from each other.

[0103] The intake section 44 incorporates an entry section 46 adjacentthe intake 25. The entry section 46 is defined by a surrounding wallstructure 54 which includes two opposed walls 55, 56, the spacingbetween which is selectively variable to permit adjustment of thecross-sectional area of the convergent section 45. In this embodiment,wall 55 is an upper wall and wall 56 is a lower wall. The surroundingwall structure 54 also includes two further opposed walls (not shown)extending between the upper and lower walls 55, 56 so as to complete aperipheral boundary around the entry section. The further side walls(not shown) are constructed to accommodate relative movement between theupper and lower walls 55, 56 upon adjustment of the cross-sectional areaof the convergent section 45. An adjustment mechanism (not shown) isprovided for selectively adjusting the spacing between the upper andlower walls 55, 56 by movement thereof towards or away from each other.

[0104] The convergent section 45, throat section 47 and divergentsection 49 are together defined by a surrounding wall structure 60 whichincludes two opposed planar walls 61, 63, the spacing between which isselectively variable to permit adjustment of the cross-sectional areathereof. In this embodiment, wall 61 is an upper wall and wall 63 is alower wall. The surrounding wall structure 60 also includes two furtheropposed walls (not shown) extending between the upper and lower walls61, 63 so as to complete a peripheral boundary around the convergent,throat and divergent sections. The further side walls (not shown) areconstructed to accommodate relative movement between the upper and lower61, 63 upon adjustment of the cross-sectional area of the divergentsection 49.

[0105] The lower wall 63 is mounted on a hinge 67 for pivotal movementtowards and away from the upper wall 61 for varying the cross-sectionalarea and the profile of the convergent, throat and divergent sections45, 47 and 49. A control means (not shown) is provided for selectivelypivoting the wall 63 about hinge 67. The control means comprises acontrol mechanism connected to the wall 63 and operate to cause it topivot about hinge 67. The control mechanism may for example comprise apower device such as a pneumatic or hydraulic ram.

[0106] The upper wall 61 of the convergent, throat and divergentsections 45, 47 and 49 is provided with a reversing flap 65 which ispivotally movable between a first position (as shown in FIG. 3) in whichit is clear of the outlet 27 and a second position (as shown in FIG. 4)in which it extends across the outlet 27 to deflect sea waterdischarging through the outlet 27. The deflected sea water imparts athrust in the opposite direction to the forward motion of the boat 13,so causing the boat to move in the reverse direction when the flap 65 isin the second position.

[0107] A driving fluid injection means 71 is provided for introducingthe driving fluid, which in this embodiment is steam, into the flowpassage 43.

[0108] The driving fluid injection means 71 includes a nozzle structure73 for injecting the steam in an expanded condition into the flowpassage 43 adjacent the upstream end of the divergent section 49. Thenozzle structure 73 is located to one side of the throat section 47,adjacent wall 51. A transition wall 75 extends between the nozzlestructure 73 and the wall 61 to provide a smooth transition between thenozzle structure 73 and the wall 61.

[0109] The nozzle structure 73 is configured as a supersonic nozzlehaving a nozzle passage 80 comprising a convergent section 81 commencingat an inlet end 83, a divergent section 87 terminating at an outlet end89, and a throat section 85 interposed between the convergent anddivergent sections.

[0110] The nozzle structure 73 comprises two elongate nozzle elements91, 93 between which the nozzle passage 80 is defined. With thisarrangement, the nozzle passage 80 comprises a slit 94 between the twonozzle elements 91, 93. The longitudinal extent of the slit 94 extendsin the longitudinal extent L of the rectangular cross-section of flowpassage 43.

[0111] Each nozzle element 91, 93 comprises a length of bar 92 having alongitudinal side 94 thereof formed with a profile corresponding to oneside of the nozzle passage 80. In this way, the longitudinal sides 94 ofthe two bars 92 co-operate to define the flow passage 80.

[0112] The two nozzle elements 91, 93 are in a spaced apart relationshipto define the nozzle passage 80 therebetween and are mounted forrelative movement towards and away from each other for varying thecross-sectional area of the nozzle passage 80. More particularly, inthis embodiment nozzle element 93 is fixed and nozzle element 91 isselectively movable laterally for varying the spacing with respect tonozzle element 93. A nozzle control means 95 is provided for selectivelymoving nozzle element 91 laterally with respect to nozzle element 93.The nozzle control means 95 may take an appropriate form, such as forexample one or more power devices such as pneumatic or hydraulic ramsoperable to cause movement of the movable nozzle element 91 with respectto the fixed nozzle element 93. The nozzle control means 95 can beoperated to move the movable nozzle element 91 during operation of thepropulsion system 21, including in particular while steam is flowingthrough the nozzle passage 80.

[0113] The inlet end 83 of the nozzle passage 80 communicates with asteam chamber 97 which has an inlet 99 for receiving steam generated bythe steam generator 31.

[0114] The steam chamber 97 has two opposed walls 101, 103 which taperinwardly towards the inlet end 83 of the nozzle passage 80. The steamchamber 97 is defined within a tubular structure 105 on which the fixednozzle element 93 is mounted. Chamber wall 101 is defined by one of thewalls of the tubular structure 105, and chamber wall 103 comprises aninternal wall provided in cavity 104 within the tubular structure 105.

[0115] Aeration means 107 are provided for aerating seawater flowingalong the flow passage 43 with an aeration gas or gaseous mixture, whichin this embodiment comprises air.

[0116] The aeration means 107 comprises a chamber 109 communicating withthe flow passage 43 via a plurality of aeration ports (not shown)upstream of the location at which steam is injected into the flowpassage 43. The aeration ports are provided by perforations in wall 51which is not only a boundary wall of the intake section 44 but also awall of the chamber 109. With this arrangement, the air is introducedinto the seawater at the intake section 44.

[0117] The air chamber 109 receives air through an air inlet 115. Airintroduced during the aeration process may be by way of an open draw orit may be regulated in order to achieve the desired level of aeration.The regulation may be achieved in any suitable way, such as byrestricting the air flow (for example by way of a valve) or enhancingthe airflow by delivering it under pressure.

[0118] The drive system 11 utilises desalinated seawater for the boiler31. Water for steam generation in the boiler 31 is extracted from thesea and processed in a desalinator of any appropriate type.

[0119] The boiler 31 is of the once through steam generation type andhas a combustion chamber 117 in which there is provided a blower 1 19for delivering combustion air into the combustion chamber 117.Combustion gases from the combustion chamber 117 pass in heat exchangerelationship with water which flows through the boiler 31 and which isconverted to steam from the hot combustion gases. After leaving theboiler 31, the spent combustion gases pass along an exhaust passage 121terminating at an exhaust outlet 123 which in this embodiment is locatedbelow the water line of the boat 13 so as to discharge into the body 14of seawater.

[0120] The exhaust gases contain remnant heat not utilised in productionof steam in the boiler 31. The heat recovery system 33 is utilised torecover some of such remnant heat in the exhaust gases, as well as torecover remnant heat in the seawater flowing along the flow passage 43after contact with the steam.

[0121] The heat recovery system 33 comprises a heat exchanger 125 inheat exchange relationship with the divergent section 49 of the flowpassage 43 and also in heat exchange relationship with the exhaustpassage 121. The heat exchanger 125 is in heat exchange contact with arefrigerant circuit 127. Heat extracted from the heat exchanger 125 byrefrigerant in the refrigerant circuit 127 is utilised for performingfurther work, as will be explained later. The refrigerant circuit 127includes a refrigerant pump 128.

[0122] The refrigerant may be of any appropriate type, such as a knownrefrigerant liquid or water at low pressure.

[0123] The heat exchanger 125 comprises an evaporator 130 defining anevaporator chamber 131 having a first wall 132 in heat exchange relationwith the flow passage 43 and a second wall 133 in heat exchange relationwith the exhaust passage 125. The first wall 132 comprises a plate 134having one face thereof confronting the flow passage 43 and an opposedface in contact with the refrigerant. The opposed face may incorporatefins (not shown) to provide an extended surface for heat transfer.Similarly, the second wall 133 comprises a plate 137 having one facethereof confronting the exhaust passage 121 and an opposed face incontact with the refrigerant. The opposed face may incorporate fins (notshown) to provide an extended surface for heat transfer. While theplates 134, 137 can be formed of any appropriate material, they arepreferably formed of cupro-nickel.

[0124] In the refrigerant circuit 127, heat is extracted from theseawater in the flow passage 43 and from the exhaust gases in theexhaust passage 121 by evaporation of the refrigerant. The resultantrefrigerant vapour drives an impeller 141 such as a turbine wheelincorporated in the refrigerant circuit, converting energy in therefrigerant vapour into torque.

[0125] The refrigerant circuit also incorporates a second heat exchanger143 positioned between the impeller wheel 141 and the evaporator 130.The second heat exchanger 143 comprises a condenser 145 having acondensing chamber 147 through which the refrigerant flows. Thecondenser 145 is so positioned as to be in contact with the seawater towhich heat is transferred upon condensation of the refrigerant.

[0126] The refrigerant circuit 127 includes flow line 149 extendingbetween the condenser 145 and the evaporator 130.

[0127] The impeller 141 is drivingly connected to a drive shaft 151 onwhich the blower 119 in the combustion chamber 117 of the boiler 31 ismounted. The drive shaft 151 is also connected to an electrodynamicmachine 153 which has two modes of operation, a first mode being as amotor in which case it drives the drive shaft 151 and thus the impeller141 and the blower 119 connected thereto, and a second mode being as analternator in which case it is driven by the drive shaft 151. Whenfunctioning as a motor, the electrodynamic machine 153 is powered by abattery 155 which may also supply electrical power to other componentryin the drive system 11, as well as to electrical and electronic deviceson the boat 13.

[0128] At commencement of the operation of the drive system 11, theelectrodynamic machine 153 operates in the first mode as a motor poweredby the battery 155. While operating as a motor, the electrodynamicdrives the blower 119 in the boiler 31. During operation of the drivesystem 11, heat develops in the exhaust gases flowing along exhaustpassage 121, and also in the seawater flowing along flow passage 43 as aconsequence of the injection of steam into the flow passage 43. Heat isextracted at the evaporator 130 by evaporation of the refrigerant, soproducing refrigerant vapour which imparts torque to the drive shaft 151through the impeller 141. The torque imparted to the drive shaft 151drives the blower 119 and also the electrodynamic machine 153 which thencommences to operate in its second mode as an alternator which chargesthe battery 155.

[0129] The propulsion system 21, boiler 31, desalinator, exhaust passage121, steam injection means 71, aeration means 107, and refrigerantcircuit 127 are incorporated in a housing 157.

[0130] Operation of the drive system 11 for propelling the boat 13 willnow be described. The boiler 31 is fired so as to commence production ofsteam. At this stage, the blower 119 in the combustion chamber 117 ofthe boiler is driven by the electrodynamic machine 153 operating in itsfirst mode as an electric a motor powered by the battery 155 of thedrive system. Spent combustion gases from the combustion chamber 117 ofthe boiler 31 pass along the exhaust passage 121 and discharge throughexhaust outlet 123 into the seawater. As the boiler 31 is of theonce-through steam generation type, it can provide a supply of steamrapidly. Once steam is available, the propulsion system 21 can operate.Initially, there is a substantially static volume of seawater in theflow passage 43 of the propulsion system 21. When propulsion isrequired, steam from the boiler 31 is introduced into the flow passage43 by way of the injection system 71. More particularly, steam isdelivered under pressure into the steam chamber 97 from where itdischarges under pressure through the nozzle structure 73 into the flowpassage 43. The nozzle structure 73 is at this stage at a settingcommensurate with the commencement of operation of the propulsion system21. Similarly, the variable cross-sectional areas of the intake section44, convergent section 45, throat section 47 and divergent section 49 ofthe flow passage 43 are also at settings commensurate with commencementof operation of the propulsion system 21. In this embodiment, steam issupplied to the nozzle structure at a temperature of about 200° C. and apressure of about 7 bar, although other steam conditions are possible.Indeed, it may be desirable in certain circumstances to provide thesteam in a superheated condition. It is also desirable for the steam,upon exiting from the nozzle structure 73, to achieve its maximumvelocity and to be fully expanded to about 1 atm.

[0131] The flow rate of the steam is set according to the desired amountof thrust to be generated. In this embodiment, mass flow rates of steamto water in a ratio of about 1:100 to 1:150 are typically utilized.

[0132] As the steam passes through the nozzle structure 73, it undergoesa reduction in pressure and an increase in velocity (typically to soniclevels), and discharges into the flow passage 43. The region of the flowpassage 43 into which the steam discharges can be considered as a mixingzone because of the mixing of the incoming steam with seawater in theflow passage 43. The high velocity steam interacts with the seawater,involving a momentum transfer to the seawater causing a flow along theflow passage 43 towards the outlet 27. Additionally, the steam condensesupon exposure to the cooling influence of the seawater. It is believedthat this rapid cooling action produces a rapid collapse or implosionwhere the steam and seawater interact. The rapid collapse or implosionof the steam provides a rapid pressure reduction at the mixing zone,drawing further seawater through the intake 25 and along the flowpassage 43 to the outlet 27. The high velocity of the steam moleculeseffects momentum transfer to the sea water flow and accelerates the seawater flow at an increased velocity, so assisting in the draw of seawater through the intake 25 and into the flow passage 43 on a continuousbasis. Forward movement of the boat 13 also assists the flow of seawaterthrough the intake 25 and along the flow passage 43.

[0133] The aeration means 107 prior to contact with the steam aeratesthe seawater flowing through the flow passage 43. Aeration -of theseawater produces a two-phase mixture which has some compressibility. Itis believed that the aeration has the effect of lowering the density ofthe two-phase mixture in comparison to the sea water, so assisting inthe transfer of the sea water along the flow passage 43 towards themixing zone. The aeration process also reduces skin friction between theseawater and the boundary surfaces of the flow passage 43.

[0134] In this embodiment, the ratio of air to water in the aerationprocess is about 1:300 by volume.

[0135] It is believed that contact between the steam and seawater at themixing zone within the flow passage 43 may also cause liberation ofgases (and oxygen in particular) from the water. The presence of suchliberated gases may assist in a reduction of frictional losses in themoving flow of seawater.

[0136] The divergent section 49 of the flow passage 43 has the effect ofcontrolling the velocity and pressure of the aerated seawater, soenhancing the thrust generated.

[0137] The thrust generated by the propulsion system 21 can beregulated. Broadly, for a low boat speed there is a requirement for alarger volume of slower moving seawater to flow along the flow passage43, and for a high boat speed there is a requirement for smaller volumeof faster moving seawater to flow along the flow passage 43. The volumeof seawater and the flow rate of the seawater can be regulated byadjustment of the various settings available within the propulsionsystem 21. More particularly, the volume of sea water flowing throughthe flow passage 43, can be regulated by adjustment of thecross-sectional areas of the intake section 44, convergent section 45,throat section 47 and divergent section 49 of the flow passage 43 aspreviously described. The flow rate of seawater can be regulated by thequantity and velocity at which steam is injected into the flow passage43 by the steam injection system 71. Additionally, the profile of theconvergent, throat and divergent sections 45, 47 and 49 of the flowpassage 43 is selectively variable by pivotal movement of the lower wall63 about hinge 67. The delivery of steam can be regulated by way of thenozzle structure 73, with the size of the nozzle passage 80 between thenozzle elements 91, 93 being adjusted as necessary in order to achievedesired steam delivery. The propulsion system 21 has the facility foralteration to the various settings which control the flow rate of thesea water along the flow passage 43 from the inlet 25 to the outlet 27at any time as is desired during operation of the drive system.Similarly, the rate of delivery of steam to the flow chamber and theextent of aeration of the seawater can be regulated as required.

[0138] The exhaust gases flowing along exhaust passage 121 containremnant heat not utilised in production of steam in the boiler 31.Additionally, seawater flowing along the flow passage 43 downstream ofthe mixing zone contains remnant heat as a result of contact with theinjected steam. The heat recovery system 33 is utilised to recover someof the heat. Specifically, the evaporator 130 is exposed to the exhaustgases in exhaust passage 121 via plate 137 and so extracts some of theheat in the exhaust gases. Similarly, the evaporator 130 is exposed tothe seawater via plate 134 and so extracts some of the remnant heat inthe seawater. The refrigerant in the refrigerant circuit 127 extractsthe heat by evaporation. The resultant refrigerant vapour is circulatedby pump 128 and contacts the impeller 141, causing rotation thereof.Rotation of the impeller 141 applies torque to the drive shaft 151, sodriving the blower 119 in the combustion chamber 117 of the boiler 31.Once the refrigerant vapour imparts sufficient torque to the drive shaft151 through the impeller 141, drive from the electrodynamic machine 153operating in its first mode as an electric motor is no longer necessary.The electrodynamic machine 153 can then convert to operation in itssecond mode in which it functions as an alternator driven by the driveshaft 151. In its capacity as an alternator, the electrodynamic machine153 charges the battery 155 from which it was previously supplied withelectric power when functioning as a motor.

[0139] From the foregoing, it is evident that the drive system 11according to the embodiment operates as a somewhat self-contained unit,apart for the need to deliver fuel for the boiler 31.

[0140] The embodiment described and illustrated is in relation to adrive system 11 operating as an outboard stern drive for a boat. Otherarrangements are, of course, possible. The drive system according to theinvention can be installed as an on-board unit on a boat.

[0141] The propulsion system forming part of the drive system 11 can beso positioned to provide stern drive, bow drive, or indeed it can bepositioned at any location between the bow and the stern of the boat.

[0142] Furthermore, the propulsion system can be so arranged that theoutlet 27 discharges into a region below the hull of the boat, resultingin aeration of water adjacent the hull. This may reduce the frictionaldrag effect on the watercraft.

[0143] Still further, two or more propulsion systems may be provided onthe watercraft on the opposed sides of the central fore-and-aft axisthereof such that the propulsion systems can be utilised to providesteering control as well as thrust to the boat.

[0144] A particular feature of the propulsion system which has beendescribed and illustrated is the low profile that is achieved by therectangular configuration of the flow passage 43 at outlet 27. Becauseof the low profile, the propulsion system 21 can conveniently bepositioned below, or incorporated into, the hull of a boat or otherwatercraft without creating unacceptable levels of drag.

[0145] While the embodiment has been described in relation to awatercraft in the form of a boat operational at sea, it is to beunderstood that the drive system may be applicable to other types ofwatercraft and that it may operate in or on bodies of water other thanthe sea, such as in or on lakes and rivers.

[0146] Referring now to FIGS. 9 and 10 of the drawings, there is shown asecond embodiment directed to a drive system 160 which is similar to thedrive system 11 according to the first embodiment in the sense that itincorporates a propulsion system 163, a steam generator 165 and a heatrecovery system 167. The steam generator 165 and the heat recoverysystem 167 operate in a similar fashion to their counterparts in thedrive system 11 according to the first embodiment.

[0147] In the second embodiment, the propulsion system 163 comprises abody structure 171 defining a flow passage 173 having an intake end 175and an outlet end 177. As was the case in the first embodiment, thepropulsion system 163 is so positioned that the intake end 175 issubmerged in the body of water on which the watercraft is supported.During operation of the propulsion system 163, water is drawn into theintake end 175 and along the passage 173 to be discharged as a jetthrough the outlet 177 to provide thrust for propelling the watercraft.

[0148] The body structure 171 includes a first portion 181 and a secondportion 182 disposed inwardly of the first portion 181. The firstportion 181 is of a generally tubular construction and includes acentral cavity 183 which is open at the ends thereof and which issurrounded by an internal wall 185. The second portion 182 is of agenerally tubular construction comprising a sidewall 187 defining acentral cavity 189 open at the ends thereof. The sidewall 187incorporates a boss section 191 in threaded engagement at 193 with thefirst portion 181. The second portion 182 is supported within the firstportion 181 by virtue of the threaded engagement at 193.

[0149] The second portion 182 extends beyond one end of the firstportion 181 and is provided with means such as a sprocket (not shown) bywhich it can be selectively rotated within the first portion 181.Because of the threaded engagement at 193 between the first and secondportions 181,182, rotation of the second portion 182 relative to thefirst portion 181 causes axial displacement of the second portion 182with respect to the first portion 181, the purpose of which will beexplained later.

[0150] The first and second portions 181 and 182 co-operate to definethe flow passage 173 as well as the intake end 175 and the outlet end177.

[0151] The cavity 189 within the second portion 182 defines an intakechamber 205 which extends from the intake 175 and terminates at adischarge opening 207 defined by the opposite end of the second portion182. The discharge opening 207 opens onto a mixing chamber 209 definedwithin the first portion 181. The cross-sectional area of the dischargeopening 207 is smaller than the cross-sectional area of the mixingchamber 209 at the location which the discharge opening 207 opens ontothe mixing chamber 209. From the mixing chamber 209, the internal wall185 of the first portion 181 is configured to define a throat 211followed by a diffuser section 212.

[0152] The end section 213 of the second portion 182 adjacent thedischarge opening 207 is spaced inwardly of the first portion 181 todefine an annular chamber 215 which opens onto the mixing chamber 209 byway of a nozzle means 217. The nozzle means 217 comprises aconvergent-divergent nozzle formation defined between an inner face 219on the internal wall 185 of the first portion 181 and an outer face 221on the second portion 182.

[0153] An aeration means 223 is provided for aerating a stream of waterdrawn into the intake 175 prior to entry of that water into the mixingchamber 209. The water is aerated by introducing an aeration gas intothe intake chamber 205. In this embodiment, the aeration gas is air. Airenters the intake chamber 205 through a plurality of aeration ports 225opening into the intake chamber. The aeration ports 225 communicate withan air cavity 227 which is defined within the body structure 171 andwhich receives air through air inlet 229. In this embodiment, the airinlet 229 is coupled to a source of air by way of an air hose (notshown).

[0154] An inlet 231 is provided for introducing a hot compressibledriving fluid into the annular chamber 215 via an opening 233 in thefirst portion 181. In this embodiment, the driving fluid is in the formof steam under pressure. From the annular chamber 215, the steam passesthrough the nozzle means 217 and enters the mixing chamber 209, the flowdirection of the steam being generally in the direction towards theoutlet 177. As the steam travels through the nozzle means 217 itundergoes a reduction in pressure and an increase in velocity (typicallyto supersonic levels) as it discharges into the mixing chamber 209. Thehigh velocity steam follows the boundary wall 210 of the mixing chamber209 by virtue of the phenomenon known as the Coanda effect and in doingso surrounds water drawn into the mixing chamber 209 from the intake175. It is believed that the steam surrounds the water stream within themixing chamber 209 and condenses upon exposure to the cooling influenceof the water so causing a rapid collapse or implosion. The rapidcollapse or implosion of the steam provides a rapid volume reduction andhence draws further water through the intake 175 and along the flowpassage.

[0155] The high velocity of the steam molecules also effect momentumtransfer to the water stream and accelerate the water stream at anincreased velocity. Consequently, water is entrained from the intake 175to the mixing chamber 209 on a continuous basis.

[0156] It is believed that contact between the steam and the water inthe mixing chamber 209 may also cause liberation of gases (and oxygen inparticular) from the water. The presence of such liberated gases isbeneficial, as described previously in relation to the first embodiment.

[0157] The mixing chamber 209 has a greater cross-sectional area thanthe cross-sectional area of the discharge opening 207 at the locationwhere the discharge opening opens onto the mixing chamber, andconsequently accommodates expansion of the aerated water entering themixing chamber through the discharge opening and providing a zone inwhich the high velocity steam can work to impart momentum upon theaerated water.

[0158] In the mixing zone 209, the water continues to accelerate withmomentum towards the throat 211 owing to the contracting configurationof the mixing chamber 209. The water increase in pressure as it passesthrough the diffuser section 212 and is assisted by the expandingbubbles arising from the aeration process as the bubbles exert pressureon the surrounding water molecules.

[0159] Thrust generated by the propulsion system 160 can be regulated bycontrolling the rate and pressure at which steam is delivered to themixing chamber 209. Further regulation may possibly be achieved byregulating the extent of aeration of the water stream delivered to themixing chamber 209. Still further regulation may possibly be achieved byvarying the characteristics of the nozzle means 217 through which steamis delivered into the mixing chamber 209. This may be accomplished byaxial displacement of the second portion 182 with respect to the firstportion 181 by rotation of the second portion as previously described.Such displacement alters the cross-sectional size of the nozzle means217.

[0160] A valve means (not shown) is incorporated in the inlet 231 forselectively diverting steam delivered to the inlet and causing it toflow in the reverse direction to normal fluid flow along the intakechamber 205 to discharge outwardly through the intake 175. In this way,the propulsion system may be utilised to provide reverse thrust to thewatercraft 13.

[0161] Steam conditions and steam and water mass flow rates are similarto those described in relation to the first embodiment.

[0162] Referring now to FIG. 11 of the drawings, there is shown apropulsion system 240 according to a third embodiment. The thirdembodiment is somewhat similar to the second embodiment, with theexception that the nozzle means 217 comprises a series of nozzles 241spaced at intervals along the mixing chamber 209 in the direction offlow along the passage 173. Furthermore, a flow control device 243 iscentrally located in the mixing chamber 209. The device 133 has an outerface 245 which defines an inner boundary surface 247 for directingincoming water into close proximity to the outer peripheral boundary ofthe mixing chamber 209 for improved contact with the steam.

[0163]FIG. 12 shows a propulsion system 250 for a drive system accordingto a fourth embodiment. The propulsion system 250 is similar to thepropulsion system 163 of the second embodiment, and additionallyincludes a flow control device 251 located in the flow control passage173. The flow control device has an outer face 253 which co-operateswith the internal wall 185 of the first portion 181 of the propulsionsystem 250 to define an annular zone 255 having a convergent region 257,a throat region 258 and a divergent region 259. The convergent region257 provides the mixing zone into which steam is injected through theannular nozzle defined by the nozzle means 217. The divergent region 259opens onto, and forms part of, the diffuser section 212.

[0164]FIG. 13 illustrates a propulsion system 260 for a drive systemaccording to a fifth embodiment. The propulsion system 260 is similar tothe propulsion system 163 of the second embodiment in the sense that itcomprises a body structure 171 having first and second portions 181, 182to define a flow passage 173 extending between an intake 175 and anoutlet 177. The intake 175 is flared at the entry section to smoothlyguide water into the flow passage 173. The flow passage 173 has anintake chamber 205 which incorporates a divergent section 261 extendingfrom the flared entry section followed by a convergent section 262opening onto the mixing chamber 207. The aeration means 223 comprises anannular air chamber 263 positioned as a sleeve about the divergingsection 261. A plurality of aeration ports 264 are provided along andcircumferentially around the divergent section 261 for introducing anaeration gas such as air into the flow passage 173.

[0165] In the embodiments which has been described, the driving fluidhas been steam. In other embodiments, the driving fluid may be amulti-phase fluid such as, for example, a mixture of steam, air andwater droplets. The air and water droplets may be entrained into thesteam as a mist. Such a multi-phase driving fluid has a higher mass flowrate than simply steam and may provide advantages.

[0166] One such embodiment is shown in FIG. 14 of the drawings. In thisembodiment, the propulsion system 265 is similar to the propulsionsystem 260 according to the previous embodiment with the exception thatthe driving fluid is a mixture of steam, air and water droplets. The airand water droplets are introduced into the steam as a mist created usingwater delivered via a water line 266 and air entrained in the water fromthe air chamber 263 via air line 267. The mist is introduced into thesteam flow at a nozzle structure 268 which includes a diverging section269. The steam transfers momentum and heat to the mist, increasing themass of the mixture. The introduction of the mist, together with thediverging section 269, provides control over the velocity of themulti-phase flow. The introduction on the air into the water flow aidsin the transfer of momentum and heat from the steam flow. The purpose ofincreasing the mass flow rate and influencing the velocity before exitfrom nozzle 268 is to allow maximum momentum and heat transfer betweenthe steam and the water and air flow mixture.

[0167] Referring now to FIG. 15 of the drawings there is shown apropulsion system 272 for a drive system according to a still furtherembodiment. The propulsion system 272 is similar to the propulsionsystem 163 according to the second embodiment in the sense that itcomprises a body structure 171 defining a flow passage 173 having anintake end 175 and an outlet end 177, with the body structure comprisinga first portion 181 and a second portion 182. In this, embodiment,however, the first and second portions 181, 182 are so configured thatthe intake end 175 and the outlet end 177′ are of substantially the samesize in terms of the cross-sectional flow area thereof. Additionally,the flow passage 173 is of substantially uniform cross-sectional sizethroughout its length, apart from some minor variation at the locationwhere the nozzle means 217 opens onto the flow passage 173, and ofsubstantially the same cross-sectional flow area as the intake end 175and outlet end 177. An annular implosion zone is established within themixing chamber 207 in the region where the two-phase mixture 274 ofwater and air contacts the injected steam.

[0168] The feature of the intake end 175 and outlet end 177 being ofsubstantially the same cross-sectional flow area, with the flow passage173 being of substantially the same cross-sectional flow area, resultsin there being no physical restriction to water flow between the intakeend 175 and outlet end 177. Such an arrangement may be advantageous incertain applications.

[0169] A particular advantage of the propulsion system 272 according tothis embodiment is that the body structure 171 presents a relativelysmall frontal area to the body of water through which it advances whenin operation, so as to reduce the effect of drag.

[0170] Referring now to FIGS. 16 and 17 of the drawings, there is showna propulsion system 270 for a drive system according to a still furtherembodiment for a watercraft such as a boat and in particular a largerboat or marine vessel.

[0171] The propulsion system 270 comprises a housing 271 defining anintake 273 and an outlet 275, with a flow passage 277 extending betweenthe intake 273 and the outlet 275. The housing 271 is generallyrectangular in cross-section, having top and bottom walls 279 and 281respectively, and sidewalls 283. A mixing zone 285 is defined within theflow passage 277.

[0172] A driving fluid injection system 287 is provided for introducinga driving fluid in the form of steam into the flow passage 277.

[0173] The driving fluid injection system 287 comprises a plurality ofsteam injection nozzles 289 at spaced intervals across the flow passage277, as shown in FIG. 13 of the drawings. The nozzles 289 are arrangedto inject steam into the mixing zone 285 in a flow direction towards theoutlet 275. Each nozzle 289 is configured as a supersonic nozzle havinga nozzle passage 291 comprising a convergent section 293, a throatsection 295, and a divergent section 297 terminating at an outlet 299opening onto the mixing zone 285.

[0174] Aeration means 301 are provided for aerating seawater flowingalong the flow passage 277 from the intake 273 to the outlet 275, withan aeration gas or gaseous mixture which in this embodiment comprisesair. The aeration means 301 comprises two aeration chambers 303 disposedonto opposed sides of the flow passage 277. Specifically, the aerationchambers 303 comprise a lower aeration chamber located adjacent thelower wall 281 and an upper aeration chamber located adjacent the upperwall 279, as shown in the drawings. Each aeration chamber 303 includes aboundary wall 305 which is exposed to the flow passage 277 and whichincludes a plurality of aeration ports 307.

[0175] The aeration chambers 303 communicate with a supply of aerationgas which in this embodiment is air. With this arrangement, air is drawninto the flow passage 277 in response to flow of seawater along the flowpassage from the intake 273 to the outlet 275. It should, however, beappreciated that, in an alternative, arrangement air may be suppliedunder pressure to the aeration chambers 303.

[0176] Each aeration chamber 303 is located upstream of the mixing zone285 with respect to the direction of flow along the flow passage 277such that sea water flowing along the flow passage 277 is aerated priorto contact with steam injected through the steam injection system 287.

[0177] The flow passage 277 includes an outlet section 278 adjacent toand terminating at the outlet 275.

[0178] Between the mixing zones 285 and the outlet section 278, the flowpassage 277 is divided into a series of separate flow paths 311 by flowcontrol elements 313 located within the housing 271. The flow controlelements 313 are located at spaced intervals across the flow passage277, as shown in FIG. 17 of the drawings. Each flow control element 313has opposed longitudinal sides 315 which include a diverging sidesection 317 and a converging side section 319. With this arrangement,the flow control elements 313 co-operate to configure each flow path 311so as to comprise a convergent section 321 and a divergent section 323.The length of the convergent section 321 is considerably greater thanthe length of the divergent section 323, as seen in FIG. 17. It willalso be noted that the two outer flow paths 311 immediately adjacent thesidewalls 283 also comprise convergent and divergent sections 321, 323,although the rate of convergence and divergence is lower as one side ofeach such flow path is defined by the respective wall 283. The divergentsections 323 open onto an outlet section 278 which terminates at theoutlet 275.

[0179] The bottom wall 281 of the housing 271 is formed in two sections,being a first wall section 341 and a second wall section 342. The twowall sections 341, 342 are spaced from each other so as to define asecondary inlet 343 through which seawater can directly enter the mixingzone 285. The first wall section 341 is movable relative to the secondwall section 342 in order to vary the size of the opening 343. A controlmeans 345 such as a pneumatic or hydraulic ram is provided for effectingrelative movement of the first wall section 341 with respect to thesecond wall section 342 so as to vary the size of the opening 343.

[0180] A reversing flap 347 is associated with the outlet 275 formovement between a first position in which it is clear of the outlet 275so as to allow normal thrust and a second position in which it extendsacross the outlet 275 so as to deflect sea water discharged therethroughso as to provide a reversed thrust action.

[0181] Operation of the propulsion system according to this embodimentwill now be described. With a static body of seawater present in theflow passage 277, steam is injected under pressure through nozzles 289into the mixing zone 285 in the direction towards the outlet 275. Highvelocity steam entering the mixing zone 285 through the nozzles 289interacts with the seawater to transfer momentum thereto, causing a flowof sea water along the flow passage 277 from the intake 273 to theoutlet 275. Additionally, the steam condenses upon exposure to thecooling influence of the seawater. It is believed that this rapidcooling action produces a rapid collapse or implosion when the steam andseawater interact. Because of the velocity at which steam is enteringthe mixing zone 285, a reduction in pressure develops in the mixing zone285. The implosion extends into the convergent sections 321 of the flowpaths 311.

[0182] The pressure reduction in the mixing zone 285 induces furtherseawater to enter the flow passage 277 through the opening 343, thevolume of which can be regulated by the control means 345.

[0183] The flow of seawater also induces air into the flow passage 277via the aeration means 301.

[0184] Aeration of the seawater produces a two-phase mixture of seawaterand air which has some compressibility.

[0185] The resultant two-phase mixture flows along the flow passage andis accelerated through the convergent sections 321 of the flow paths 311before entering divergent sections 323 where the velocity slows and thepressure increases, so as to provide enhanced thrust at the outlet 275.

[0186] Referring now to FIG. 18 of the drawings, there is shown apropulsion system according to a further embodiment which is similar tosome respects to the previous embodiment 270, with the exception thatthere is incorporated a second stage for the purposes of furtherenhancing thrust developed by the propulsion system.

[0187] The propulsion system 350 comprises a housing 351 defining anintake 353 and an outlet 355, with the flow passage 357 extendingbetween the intake 353 and the outlet 355.

[0188] The housing 351 is formed in various sections, comprising a firstsection 361, a second section 362, a third section 363 and a fourthsection 364.

[0189] A mixing zone 365 is defined within the flow passage 357 withinthe first section 361.

[0190] A driving fluid injection system 369 is provided for introducinga driving fluid in the form of steam into the flow passage 357. Thedriving fluid injection system 369 comprises a plurality of steaminjection nozzles 371 at spaced intervals across the flow passage 357,as shown in the drawing. The nozzles 371 are arranged to inject steaminto the mixing zone 365 in a flow direction towards the outlet 355.Each nozzle 371 is configured as a supersonic nozzle having a nozzlepassage 373 comprising a convergent section 375, a throat section 377,and a convergent section 379 opening onto the mixing zone 365.

[0191] An aeration means 381 is provided for aerating seawater flowingalong the flow passage 357 from the intake 353 to the outlet 355. Theaeration means 381 is of a similar construction to the aeration means inthe previous embodiment.

[0192] Between the mixing zone 365 and the second housing section 362,the flow passage 357 is divided into a series of separate flow paths 391by flow control elements 393 located within the first section 361 of thehousing. The flow control elements 393 are located at spaced intervalsacross the flow passage 357 within the first housing section 361, asshown in FIG. 18. Each flow control element 393 has opposed longitudinalsides 395 which diverge in the direction of fluid flow so as toconfigure each flow path 391 as a convergent flow path.

[0193] The convergent flow paths 391 open onto a chamber 401 definedwithin the second housing section 362.

[0194] Openings 403 communicate with the chamber 401 for directentrainment of additional seawater into the chamber. A control means(not shown) is provided for regulating the extent of flow through theopenings 403.

[0195] Steam nozzles 406 are provided for injection supplementary steaminto chamber 401 in a flow direction towards outlet 355.

[0196] Secondary flow control elements 405 are positioned within theregion defined within the second and third housing sections 362 and 363respectively.

[0197] Each secondary flow control element 405 has opposed longitudinalside walls 407 which include a diverging section 409 located in thesecond housing section 362 and a diverging section 411 located in thethird housing section 363. With this arrangement, the secondary flowcontrol elements 405 co-operate to establish a series of flow paths 413within the common region between the second and third housing sections362, 363. The flow control elements 405 co-operate to configure eachflow path 413 to comprise a convergent section 414 in the second housingsection 362 and a divergent section 416 in the third housing 363.

[0198] The sidewalls 415 of the second and third housing section 362,363 are appropriately angled to complement the configuration of the flowpaths 413.

[0199] The flow paths 413 open onto the fourth housing section 364 whichterminates at the outlet 355. The fourth housing section 364 isconfigured so as to define a divergent section terminating at the outlet355.

[0200] Operation of the propulsion system according to this embodimentwill now be described. With a static volume of seawater present in theflow passage 357, steam is injected under pressure through the nozzles373 into the mixing zone 365 in the direction towards the outlet 355.High velocity steam entering the mixing zone 365 through the nozzles 373interacts with the seawater to transfer momentum thereto, causing a flowof sea water along the flow passage 357 from the intake 353 to theoutlet 355. Additionally, the steam condenses upon exposure to thecooling influence of the seawater. A flow of seawater along the flowpassage 357 from the intake 353 is established, for reasons explained inrelation to the previous embodiment.

[0201] The two phase mixture resulting from aeration of the sea waterflows along the passage 357 and is accelerated through the convergentflow paths 391 before entering the secondary chamber 362, where furthersea water is entrained through openings 403. Additionally, supplementarysteam is injected through steam nozzles 406. A secondary implosiondevelops in the secondary chamber 362, particularly in the convergingflow paths 414. The flow is further accelerated in the convergingsections 414 and then expanded in the diverging sections 416 to developa flow of desired velocity and pressure which exits through the outlet355 to provide thrust.

[0202] As the flow of sea water between the intake 353 and 355 issubjected to various stages of momentum transfer through contact withsteam, it is believed that the energy in the steam is better utilised todevelop thrust at the outlet 355 for propulsion.

[0203] In the embodiments which have been described, the propulsionsystem according to the invention has been applied to propulsion ofwater craft. Other applications are, of course, possible. One such otherapplication is as a pump.

[0204] Referring now to FIG. 19, there is shown a drive system 450according to a further embodiment for a boat 451 having a stern 453 andhull 455. The drive system 450 incorporates a propulsion system 460comprising a body structure 461 defining a flow passage 463 having anintake 465 and an outlet 467.

[0205] The intake 465 opens onto the hull 455 of the boat 451 so as tobe exposed to the seawater on which the boat in accommodated. The intake465 is of generally rectangular configuration in this embodiment.

[0206] The body structure 461 comprises an eductor tube 471 extendingfrom the intake 465. The other end of the tube 471 is of generallycircular configuration and is surrounded by a shroud 473. The shroud 473defines a mixing chamber 475 adjacent the end of the tube 471 and adiffuser section 477 which extends to, and opens onto, the outlet 467.The shroud 473 has a wall 481 which is spaced from the tube 471 suchthat an annular nozzle means 483 is defined through which a drivingfluid in the form of steam can be injected into the mixing chamber 475.Steam is delivered to a region 485 upstream of the nozzle means 483 viaa steam delivery line 487.

[0207] An aeration means 489 is provided adjacent the intake 465. Theaeration means 489 comprises an aeration chamber 491 positioned aroundthe perimeter of the intake 465 and a plurality of aeration ports 493extending between the chamber 491 and the flow passage 463. A deliveryline 494 is provided for delivering aeration gas such as air to theaeration chamber 491.

[0208] The propulsion system 460 operates in a similar fashion toembodiments described previously in that high velocity steam injectedinto the mixing chamber 475 through the nozzle means 483 interacts withseawater in the flow passage 461, involving a momentum transfer to theseawater causing a flow along the flow passage 461 towards the outlet467. Additionally, the steam condenses upon exposure to the coolinginfluence of the seawater to produce a rapid collapse or implosion,causing a suction effect which draws seawater along the flow passage 463from the intake 465. The injected steam tends to follow the innersurface of the shroud wall 481 by virtue of the Coanda effect which aidsin reducing the skin friction against the wall surface. The aeradedseawater may also have a reaction effect in the diffuser section 477which further enhances propulsion. Forward movement of the boat 451 alsoassists the flow of seawater through the intake 465 and along the flowpassage 463. In particular, as the bow of the boat progressively liftswith increasing boat speed, the intake 465 is increasingly exposed tooncoming seawater as the boat moves forwardly, so increasing the flowinduced along the flow passage 461 by relative movement between the boat451 and the seawater. The propulsion effect provided by the injectedsteam enhances the flow and provides thrust.

[0209] A particular feature of this embodiment is that the bodystructure 461 extends rearwardly of the stern 453 of the boat 451 andpresents minimal frontal area to the oncoming water as the boat movesforwardly, so limiting the effect drag.

[0210] It has been found that good performance can be achieved bypositioning the outlet 467 such that it is just below the waterline whenthe boat 451 is in operation. With the outlet 467 in this position, itcan intermittently extend above the water line as a result of wavemotion and movement of the boat 451. The intermittent exposure of theoutlet 467 above the waterline has been found to be beneficial incertain operating conditions in terms of the thrust that is developed.

[0211]FIG. 20 of the drawings illustrates a propulsion system 500according to a further embodiment utilised at a pump for pumping liquidssuch as water from a body 501 of such liquid contained within areservoir 503. The propulsion system 500 is of similar construction tothe propulsion system 163 according to the second embodiment, andaccordingly corresponding reference numerals are used to identifycorresponding parts.

[0212] The pump provided by the propulsion system 500 is incorporated ina pipeline 507 having a pipe section 509 extending between the reservoir503 and the pump intake 175. The pipeline 507 has a further pipe section511 extending from the pump outlet 177.

[0213] Operation of the propulsion system 500 as a pump is similar tooperation of propulsion system 163, drawing a stream of liquid from thereservoir 503 and pumping it along the pipeline 507.

[0214] Where the pump is used in a fire-fighting application, theaeration gas may be a gas or gaseous mixture of a type which wouldassist in extinguishing the fire, such as for example an inert gas.

[0215] A particular feature of the propulsion systems according to theinvention is that flow along the flow passage from the intake to theoutlet is established and maintained without the use of an impeller.Furthermore, it is not necessary to provide an impeller or othermechanical device to deliver fluid to the flow passage intake. Fluid cansimply be drawn through the intake. In certain applications, such as inpropulsion of watercraft, fluid flow along the flow passage issupplemented by relative movement between the propulsion system and thebody of fluid, with such relative movement inducing flow along the flowpassage.

[0216] It should be appreciated that the scope of the invention is notlimited to the scope of the embodiments described.

[0217] Throughout the specification, unless the context requiresotherwise, the word “comprise” or variations such as “comprises” or“comprising”, will be understood to imply the inclusion of a statedinteger or group of integers but not the exclusion of any other integeror group of integers.

The claims defining the invention are as follows
 1. A propulsion systemcomprising a flow passage having an intake for communicating with asource of working fluid and outlet, a mixing zone disposed within theflow passage between the intake and the outlet, means for introducing ahot compressible driving fluid into the mixing zone, whereby interactionbetween the driving fluid and the working fluid in the mixing zonedevelops a pressure reduction in the mixing zone to cause working fluidto be drawn from said source into the mixing zone and propelled towardsthe outlet, and means for aerating the working fluid with an aeratinggas prior to interaction of the driving fluid in the mixing zone wherebya three-phase fluid regime is created in the mixing zone by virtue ofthe interaction of the aerating gas, the working fluid and the drivingfluid.
 2. A propulsion system according to claim 1, in which the meansfor aerating the working fluid are prior to the introduction of thedriving fluid.
 3. A propulsions system according to claim 2, in whichthe means for aerating the working fluid are prior to the mixing zone.4. A propulsion system according to any one of claims 1 to 3, in whichthe means for introducing driving fluid comprise means for injecting thedriving fluid.
 5. A propulsion system according to any one of claims 1to 4 wherein the driving fluid is introduced in a flow direction towardsthe outlet.
 6. A propulsion system according to claims 1 to 5 whereinthe driving fluid is introduced into the mixing zone at a temperature ofat least 50° C. above the temperature of the working fluid
 7. Apropulsion system according to claim 6 wherein the driving fluid isintroduced into the mixing chamber at a temperature more than about 70°C. above the temperature of the working fluid.
 8. A propulsion systemaccording to claims 1 to 7 wherein the interaction between the drivingfluid and the working fluid provides momentum transfer from the drivingfluid to the working fluid.
 9. A propulsion system according to any oneof claims 1 to 8 wherein the working fluid comprises a liquid.
 10. Apropulsion system according to claim 9 wherein the liquid compriseswater.
 11. A propulsion system according to claim 9 or 10 whereincontact between the driving fluid and the working fluid at the mixingzone within the flow passage causes liberation of gases from the workingfluid.
 12. A propulsion system according to any one of the precedingclaims wherein the compressible driving fluid comprises a substantiallygaseous fluid capable of rapid pressure reduction upon exposure to thecooling influence of the working liquid.
 13. A propulsion systemaccording to claim 12 wherein the driving fluid comprises a condensablevapour
 14. A propulsion system according to claim 13 wherein thecondensable vapour comprises steam.
 15. A propulsion system according toclaim 12 wherein the driving fluid comprises exhaust gas from acombustion process
 16. A propulsion system according to any one ofclaims 1 to 14 wherein the driving fluid is steam and the working fluidis water, and wherein the mass flow rates of steam to water are in aratio ranging from about 1:10 to 1:150.
 17. A propulsion systemaccording to any one of the preceding claims wherein the aeration meanscomprises a plurality of aeration nozzles circumferentially spaced aboutand opening onto the flow passage.
 18. A propulsion system according toany of the preceding claims wherein the flow passage is configured tocause induction of the aeration gas into the flow passage.
 19. Apropulsion system according to any one of the preceding claims furthercomprising means for selectively controlling the aerating of the workingfluid.
 20. A propulsion system according to any one of the precedingclaims wherein the aerating gas comprises air.
 21. A propulsion systemaccording to any one of the preceding claims wherein the working fluidcomprises water and the aerating gas comprises air, and wherein theratio of air to water is not more than about 1:10 by volume.
 22. Apropulsion system according to claim 21 wherein the ratio of air towater is about 1:300.
 23. A propulsion system according to any one ofthe preceding claims wherein a section of the flow passage between theintake and the mixing zone defines an intake passage terminating at adischarge opening from which the working fluid expands upon entry intothe mixing zone.
 24. A propulsion system according to claim 23 whereinthe discharge opening has a cross-sectional area smaller than thecross-sectional area of the mixing zone at the location where thedischarge opening opens onto the mixing zone.
 25. A propulsion systemaccording to any one of the preceding claims wherein the mixing zoneprogressively contracts in the direction of fluid flow therethrough. 26.A propulsion system according to claim 25 wherein the mixing zonecontracts to a size creating a choked flow condition in the flowpassage.
 27. A propulsion system according to any one of the precedingclaims wherein the means for introducing driving fluid comprises anozzle means through which the driving fluid is introduced into themixing zone.
 28. A propulsion system according to claim 27 wherein thenozzle means is disposed adjacent a boundary surface of the flowpassage.
 29. A propulsion system according to claim 28 wherein thenozzle means extends around a perimeter of the flow passage.
 30. Apropulsion system according to claim 27, 28 or 29 wherein the nozzlemeans comprises a nozzle passage.
 31. A propulsion system according toclaim 30 wherein the nozzle passage of annular configuration.
 32. Apropulsion system according to claim 31 wherein the annular nozzlepassage is defined between first and second members within which theflow passage is defined, the first and second members being selectivelymovable with respect to each other for varying the size of the nozzleflow passage.
 33. A propulsion system according to claim 32 wherein thefirst member defines the mixing zone and the second member defines theintake passage opening onto the mixing zone, the annular nozzle passagebeing disposed around the discharge opening of the intake passage.
 34. Apropulsion system according to claim 30 wherein the nozzle passageconfigured as a slit.
 35. A propulsion system according to claim 34wherein the nozzle passage is defined between two spaced apart elongatenozzle elements.
 36. A propulsion system according to claim 35 whereinthe two nozzle elements are movable relative to each other forselectively varying the size of the nozzle passage therebetween.
 37. Apropulsion system according to claim 36 further comprising a nozzlecontrol means operable to move the nozzle sections relative to eachother.
 38. A propulsion system according to any one of claims 27 to 37wherein the nozzle means comprises a supersonic nozzle.
 39. A propulsionsystem according to any of claims 30 to 38 wherein the nozzle passagehas a boundary wall defined by a surface extending beyond the nozzlepassage to provide a guide surface along which driving fluid issuingfrom the nozzle passage can flow.
 40. A propulsion system according toclaim 39 wherein said surface extends beyond the nozzle passage todefine a boundary wall of the mixing zone.
 41. A propulsion systemaccording to any one of claims 27 to 38 wherein the nozzle meanscomprises axially spaced nozzles.
 42. A propulsion system according toany one of the preceding claims wherein the flow passage comprises anoutlet section terminating at the outlet, the outlet being configured asa diffuser.
 43. A propulsion system according to any one of thepreceding claims wherein the flow passage comprises a portion definedbetween two opposed surfaces at least one of which is selectivelymovable relative to the other for varying the cross-sectional area ofthe portion of the flow passage defined therebetween.
 44. A propulsionsystem according to claim 43 wherein said portion of the fluid flowpassage includes said outlet section.
 45. A propulsion system accordingto claim 43 or 44 wherein the two opposed surfaces are substantiallyplanar surfaces
 46. A propulsion system according to claim 43, 44 or 45wherein the two opposed surfaces are angularly movable relative to eachother.
 47. A propulsion system according to any one of claims 43 to 46further comprising an outlet control means operable to control relativemovement between the two opposed surfaces.
 48. A propulsion systemaccording to any one of the preceding claims further comprising meansfor selectively diverting the driving fluid to cause flow thereof in areverse direction along the flow passage for discharge outwardly throughthe intake.
 49. A propulsion system according to any one of thepreceding claims further comprising means operable to selectively varythe size of the intake.
 50. A propulsion system according to any one ofclaims 1 to 41 wherein the intake and the outlet are of substantiallythe same cross-sectional flow area.
 51. A propulsion system according toclaim 50 wherein the flow passage is of substantially the samecross-sectional flow area throughout the length thereof between theintake and the outlet.
 52. A propulsion system comprising a flow passagehaving an intake for communicating with a source of working liquid andan outlet, a mixing zone disposed within the flow passage between theintake and outlet, aeration means for aerating the working liquid withan aerating gas before delivery thereof to the mixing chamber, and anozzle means for introducing a jet of hot compressible driving fluidinto the mixing zone in a flow direction towards the outlet whereby athree-phase fluid regime is created in the mixing zone by virtue of theinteraction of the aerating gas, the working liquid and the drivingfluid, and whereby interaction between the driving fluid and the workingliquid in the mixing zone develops a pressure reduction relative to theintake pressure to cause working liquid to be drawn from said sourceinto the mixing zone and propelled towards the outlet.
 53. A propulsionsystem comprising a flow passage having an intake for communicating witha source of working fluid and an outlet, a mixing zone disposed withinthe flow passage between the intake and outlet, and a nozzle means forinjecting a condensable vapour into the nixing zone in a flow directiontowards the outlet, whereby interaction between the condensable vapourand the working liquid in the mixing zone causes the vapour to condenseproviding a volume reduction to create a suction effect to cause workingliquid to be drawn from said source into the mixing zone and propelledtowards the outlet, and means for aerating the working fluid with anaerating gas prior to interaction of the driving fluid in the mixingzone whereby a three-phase fluid regime is created in the mixing zone byvirtue of the interaction of the aerating gas, the working fluid and thecondensable vapour.
 54. A propulsion system according to claim 52wherein the condensable vapour comprises steam
 55. A propulsion systemaccording to claim 53 or 54 wherein the working fluid comprises aliquid.
 56. A propulsion system for a watercraft accommodated on or in abody of water, the propulsion system comprising a flow passage having anintake for communicating with the body of water and an outlet, a mixingzone disposed within the flow passage between the intake and outletwhereby a stream of water drawn from the body of water through theintake as a working fluid can enter the mixing zone, and an injectionmeans for injecting a hot compressible driving fluid into the mixingzone in a flow direction towards the outlet, whereby interaction betweenthe driving fluid and the water in the mixing zone develops a zone ofreduced pressure to cause a stream of water to be drawn from the body ofwater into the mixing zone and propelled towards the outlet, and meansfor aerating the water with an aerating gas prior to interaction of thedriving fluid in the mixing zone whereby a three-phase fluid regime iscreated in the mixing zone by virtue of the interaction of the aeratinggas, the water and the driving fluid.
 57. A propulsion system accordingto any one of the preceding claims wherein the flow passage is devoid ofany obstruction therein likely to substantially impede flow through theflow passage.
 58. A propulsion system according to any one of claims 1to 56 wherein a flow control device is located in the mixing zone.
 59. Apropulsion system according to any one of claims 1 to 58 wherein thedriving fluid is introduced into an inner region of the working fluidflow.
 60. A propulsion system according to claim 59 wherein the nozzlemeans opens into the flow passage inwardly of a boundary wall thereof.61. A propulsion system according to any one of the preceding claimsfurther comprising means for admission of further working fluid into theflow passage after introduction of the driving fluid thereinto, whichfurther working fluid is entrained in the flow along the flow passage.62. A propulsion system according to claim 61 where the means foradmission of further working fluid comprises at least one openingproviding direct communication between the source of working fluid andthe flow passage.
 63. A propulsion system for a watercraft accommodatedon or in a body of water, the propulsion system comprising a flowpassage having an intake for communicating with the body of water and anoutlet, a mixing zone disposed within the flow passage between theintake and outlet whereby a stream of water drawn from the body of waterthrough the intake can enter the mixing zone, and for introducing a hotcompressible driving fluid into the mixing zone, whereby interactionbetween the driving fluid and the water in the mixing zone develops azone of reduced pressure to cause a stream of water to be drawn from thebody of water into the mixing zone and propelled towards the outlet, andmeans for aerating the working fluid with an aerating gas prior tointeraction of the driving fluid in the mixing zone whereby athree-phase fluid regime is created in the mixing zone by virtue of theinteraction of the aerating gas, the water and the driving fluid, thepropulsion system being devoid of an impeller or other mechanical devicefor generating fluid flow along the flow passage to provide thrust atthe outlet.
 64. A watercraft having a propulsion system according to anyone of the preceding claims.
 65. A watercraft according to claim 64wherein the intake and outlet are each positioned as to in use open intothe body of water on or in which the watercraft is accommodated.
 66. Awatercraft according to claim 65 wherein the outlet is so positionedthat it is intermittently exposed above the water surface during forwardpropulsion of the watercraft.
 67. A watercraft according to claim 64, 65or 66 wherein the outlet is positioned to discharge driving fluidtherefrom at a location underneath the hull of the watercraft.
 68. Adrive system for a watercraft, the drive system comprising a propulsionsystem according to any one of claims 1 to
 63. 69. A drive system for awatercraft adapted to be accommodated on or in a body of water, thedrive system comprising a steam generator for generating a supply ofsteam, and a propulsion system, the propulsion system comprising a flowpassage having an intake for communicating with the body of water and anoutlet, a mixing zone disposed within the flow passage between theintake and the outlet whereby a stream of water drawn from the body ofwater through the intake can enter the mixing zone, and an injectionmeans for injecting steam generated by the steam generator into themixing zone in a flow direction towards the outlet, whereby interactionbetween the steam and the water in the mixing zone causes water to bedrawn from the body of water into the mixing zone and propelled towardsthe outlet, and means for aerating the water with an aerating gas priorto interaction of the steam in the mixing zone whereby a three-phasefluid regime is created in the mixing zone by virtue of the interactionof the aerating gas, the water and the steam
 70. A drive systemaccording to claim 69 further comprising a heat recovery system adaptedto recover remnant heat in the body of water arising from contact withthe steam.
 71. A drive system according to claim 69 or 70 wherein thesteam generator comprises a boiler adapted to generate heat fromcombustion of a fuel, the heat recovery means being adapted to alsorecover at least some remnant heat in combustion gases from the boiler.72. A method of generating a fluid flow comprising the steps of:providing a flow passage having an intake and an outlet, locating theintake of the flow passage to communicate with a source of primary fluidfrom which the fluid flow is to be established; and introducing adriving fluid into the flow passage for interacting with primary fluidin the flow passage to develop a pressure reduction at a zone in theflow passage to cause primary fluid to be drawn from said source intosaid zone and propelled towards the outlet; and further comprising thestep of aerating the primary fluid with an aerating gas prior to theintroduction of the driving fluid into the primary fluid whereby athree-phase fluid regime is created in the flow passage by virtue of theinteraction of the aerating gas, the primary fluid and the drivingfluid.
 73. A method of generating a fluid flow comprising the steps of:providing a flow passage having an intake and an outlet; locating theintake of the flow passage to communicate with a source of fluid fromwhich the fluid flow is to be established; and injecting a condensablevapour into the flow passage for interacting with fluid therein toprovide a volume reduction upon condensation of the vapour to create asuction effect at a zone in the flow passage to cause fluid to be drawnfrom said source into said zone and propelled towards the outlet; andfurther comprising the step of aerating the fluid with an aerating gasprior to the introduction of the condensable vapour into the fluidwhereby a three-phase fluid regime is created in the flow passage byvirtue of the interaction of the aerating gas, the fluid and thecondensable vapour.
 74. A method of propelling a watercraft through abody of water, the method comprising the steps of: providing thewatercraft with a flow passage having an intake and an outlet bothopening onto the body of water; and introducing a driving fluid into theflow passage to develop a pressure reduction at a zone in the flowpassage to cause water from the body of water to be drawn through theinlet into said zone and propelled towards the outlet as a stream forpropelling the watercraft; and further comprising the step of aeratingthe water with an aerating gas prior to the introduction of the drivingfluid into the water whereby a three-phase fluid regime is created inthe flow passage by virtue of the interaction of the aerating gas, thewater and the driving fluid
 75. A method of propelling a watercraftthrough a body of water, the method comprising the steps of: providingthe watercraft with a flow passage having an intake and an outlet bothopening onto the body of water; and introducing a condensable vapoursuch as steam into the flow passage to provide a volume reduction uponcondensation of the vapour and thereby create a suction effect at a zonein the flow passage to cause water from the body of water to be drawnthrough the inlet into said zone and propelled towards the outlet as astream for propelling the watercraft; and further comprising the step ofaerating the water with an aerating gas prior to the introduction of thecondensable vapour into the water whereby a three-phase fluid regime iscreated in the flow passage by virtue of the interaction of the aeratinggas. the water and the condensable vapour.
 76. A pump comprising apropulsion system according to any one of claims 1 to
 55. 77. Apropulsion system according to any one of claims 1 to 63, comprising asystem for recovering heat from a heat source, the heat recovery systemcomprising a refrigerant circuit having a heat exchanger exposed to theheat source for extracting heat therefrom to vapourise a refrigerant inthe refrigerant circuit, and means associated with the refrigerantcircuit for converting heat energy in the vapourised refrigerant totorque.
 78. A drive system for a watercraft accommodated on or in a bodyof water, the drive system comprising a propulsion system according toclaim 14, a boiler for generating a supply of steam, the boiler having acombustion chamber and an exhaust passage along which exhaust gases fromthe combustion chamber are discharged, and a heat recovery system forrecovering remnant heat in the exhaust gases, the heat recovery systemcomprising a refrigerant circuit having a heat exchanger exposed to theexhaust passage for extracting heat from the exhaust gases to vapourisea refrigerant in the refrigerant circuit, and means associated with therefrigerant circuit for converting heat energy in the vapourisedrefrigerant to torque.
 79. A drive system for a watercraft accommodatedon or in a body of water, the drive system comprising a propulsionsystem according to claim 14, and a heat recovery system for recoveringremnant heat in the water flowing along the flow passage after theintroduction of steam into the water, the heat recovery systemcomprising a refrigerant circuit having a heat exchanger exposed to theflow passage for extracting heat from water flowing along the flowpassage to vapourise a refrigerant in the refrigerant circuit, and meansassociated with the refrigerant circuit for converting heat energy inthe vapourised refrigerant to torque.
 80. A drive system for awatercraft accommodated on or in a body of water, the drive systemcomprising a boiler for generating a supply of steam, the boiler havinga combustion chamber and an exhaust passage along which exhaust gasesfrom the combustion chamber are discharged, a propulsion systemaccording to claim 14, and a heat recovery system for recovering remnantheat in the exhaust gases and in the water flowing along the flowpassage after introduction of steam into the water, the heat recoverysystem comprising a refrigerant circuit having a heat exchanger exposedto the exhaust passage and the flow passage for extracting heat from theexhaust gases and the water respectively to vapourise a refrigerant inthe refrigerant circuit, and means associated with the refrigerantcircuit for converting heat energy in the vapourised refrigerant totorque.
 81. A drive system according to claim 80 wherein the refrigerantcircuit includes an evaporator having a first portion thereof exposed tothe exhaust passage for extracting heat from the combustion gasespassing therealong and a second portion exposed to the flow passage forextracting heat from water flowing therealong.
 82. A nozzle means inaccordance with a propulsion system according to any one of claims 1 to63 having an inlet, an outlet and a flow passage extending between theinlet and the outlet, characterised in that the size of the flow passageis selectively variable.
 83. A nozzle means according to claim 82comprising a convergent section, a throat section and a divergentsection, the convergent section extending from the inlet to the throatsection and the divergent section extending from the throat section tothe outlet.
 84. A nozzle means according to claim 82 or 83 comprising anozzle structure having two elongate elements between which the nozzlepassage is defined.
 85. A nozzle means according to claim 84 wherein thetwo nozzle elements are movable relative to each other for selectivelyvarying the size of the flow passage therebetween.
 86. A propulsionsystem comprising a flow passage having an intake for communication witha source of working fluid and an outlet, a mixing zone disposed withinthe fluid passage between the intake and the outlet, a nozzle means forintroducing a jet of driving fluid into the mixing zone in a flowdirection towards the outlet, whereby interaction between the drivingfluid and the working fluid in the mixing zone causes working fluid tobe drawn from the source into the mixing zone and propelled towards theoutlet, the nozzle means having a nozzle passage of selectively variablesize, and means for aerating the working fluid with an aerating gasprior to interaction of the driving fluid in the mixing zone whereby athree-phase fluid regime is created in the mixing zone by virtue of theinteraction of the aerating gas, the working fluid and the drivingfluid.
 87. A drive system for a watercraft adapted to be accommodated onor in a body of water, the propulsion system comprising a flow passagehaving an intake for communicating with the body of water and an outlet,a mixing zone disposed within the flow passage between the intake andthe outlet whereby a stream of water drawn from the body of waterthrough the intake can enter the mixing zone, and a nozzle means forintroducing a jet of driving fluid into the mixing zone in the flowdirection towards the outlet, whereby interaction between the drivingfluid and water causes water to be drawn through the intake from thebody of water and propelled towards the outlet, the nozzle means havinga nozzle passage of selectively variable size, and means for aeratingthe working fluid with an aerating gas prior to interaction of thedriving fluid in the mixing zone whereby a three-phase fluid regime iscreated in the mixing zone by virtue of the interaction of the aeratinggas, the water and the driving fluid.
 88. A drive system for awatercraft adapted to be accommodated on or in a body of water, thedrive system comprising a steam generator for generating a supply steam,a propulsion system comprising a flow passage having an intake forcommunication with the body of water and an outlet, a mixing zonedisposed within the flow passage between the intake and outlet whereby astream of water drawn from the body of water through the intake canenter the mixing zone, and a steam nozzle means for introducing steaminto the mixing zone in a flow direction towards the outlet, wherebyinteraction between the steam and the water causes water to be drawninto the flow passage through the intake and propelled towards theoutlet, the steam nozzle means having a flow passage of selectivelyvariable size, and means for aerating the working fluid with an aeratinggas prior to interaction of the driving fluid in the mixing zone wherebya three-phase fluid regime is created in the mixing zone by virtue ofthe interaction of the aerating gas, the water and the steam.